Attention

IronPLC can only run very simple programs. The steps described are accurate but many language features are not yet supported.

RS

Reset-dominant bistable function block. A flip-flop where the reset input takes priority: if both S and R1 are TRUE, the output Q1 is FALSE.

IEC 61131-3	Section 2.5.2.3.1
Support	Not yet supported

Inputs

Name	Type	Description
S	BOOL	Set input
R1	BOOL	Reset input (dominant)

Outputs

Name	Type	Description
Q1	BOOL	Output state

Behavior

The output Q1 is set to TRUE when S is TRUE, and reset to FALSE when R1 is TRUE. Because the reset input is dominant, if both S and R1 are TRUE simultaneously, the output Q1 is FALSE. The output retains its value between scans.

Example

VAR
  latch1 : RS;
  set_signal : BOOL;
  reset_signal : BOOL;
  output : BOOL;
END_VAR

latch1(S := set_signal, R1 := reset_signal);
output := latch1.Q1;

See Also

• SR — set-dominant bistable